Safety glass



June 19, 1934. G, B. wATKlNs SAFETY GLASS Fle'd June- 25, 1931 Snventor 55 an autoclave, and

Patented June 19, 193'4 PATENT oFFlcE SAFETY GLASS George B. Watkins, Toledo,

Libbey-Owens-Ford Glass Company,

Ohio, assigner to Toledo,

Ohio, a corporation of Ohio Application ,lune 25, 1931, Serial No. 546,751

9 claims.

The present invention relates to the' art of safety glass manufacture and more particularly to an improved bonding medium. The expression safety glass is used to designate a composite structure usually consisting of two or more sheets of glass with one or more interposed non-brittle layers, for example, pyroxylin plastic sheets. The value of such-a composite structure is dependent, among other things, upon the adequacy and permanency of the bond between the laminations, clearness of vision including freedom from dirt, and stability of the sheet. It is an object of the present invention to provide a processl for producing an improved safety glass wherein the bond inducing medium or bonding agent can be applied easily and by mechanical means if desired. 'I'he invention also contemplates the use of a bonding agent including a mixture of a water soluble adhesive, for example, gelatin and a solvent therefor, for example, di-

ethylene glycol, which mixture or solution, after it has been properly reacted, has added thereto a diluent, preferably water. The mixture, after it has been applied to the laminations, does not require drying or seasoning, thereby' reducing the possibility of introduction of dirt between the laminations. By the use of my improved mixture and method of application thereof, the resultant composite sheet possesses an exceptionally tenacious bond, the sheet is exceedingly stable, `and clear to vision. Further, by the use of the present invention; the cost of manufacturing safety glass is comparatively low because of the relatively few operations required. y

Other objects and advantages of the invention will become more apparent during the course of the following description when taken in connec- -tion with the accompanying drawing.

In the drawing wherein like numerals are ernployed to designate like parts throughoutv the same,

Fig. 1 is a vertical longitudinal section through one form of machine that can be used in applying my improved mixture to the laminat-ions.-

Fig. 2 is a fragmentary sectional view of the laminations in proper superimposed relationship but shown spaced from one another.` for purposes of illustration,

Fig.- 3 is a fragmentary vertical longitudinal section, through -a form of device that can 'be used in-pressing the laminations together,

.'Fig.- 4 isja. diagrammatic representation of a platen press,

Fig. 5 is a vertical transverse section through plastic.

6 lis a fragmentary sectional view of a finished sheet of safety glass.

Referring to Fig. 2, the numerals 11 and 12 designate two sheets of glass between which is arranged a plastic sheet 13 which may be any cellulose composition material, for example, pyroxylin plastic. As is shown in Fig. 2, each of the glass sheets hasa coating 14 thereon.` The present invention has particular reference to the coating 14.

It is an'aim of the present invention to provide a bonding agent that will act not onlyas an adhesive between the laminations, but will also include a solvent or mixture of solvents adapted to act upon the layer -13.

Another important feature of the invention is to provide a bonding agent giving a process which will accommodate pyroxylin plastic sheet made throughout the different seasonal periods of the year and to produce a laminated product having a satisfactory bond regardless of the time of the year the pyroxylin plastic is manufactured and used. Broadly, the present mixture possesses a Water soluble adhesive which will give a satisfactory bond when the stock has a considerable amount of moisture present during the summer months and at the same time the bonding agent includes a solvent that will give a so-called nitrocellulose bond which theoretically, at least, will predominate in the fall and winter months when the plastic, as received, is fairly free vof moisture'.4

However, in the preferred embodiment of the invention, all of the pyroxylin plastic used is subjected to a treatment whereby to control, within reasonable limits, the moisture content of the Such treatment will tend to give substantially uniform results throughout the year.

To produce my improved bonding agent, a

water soluble adhesive, for example, gelatin, 1S

reacted in a pyroxylin 'plastic solvent, for example, diethylene glycol. To assist in the reaction,

,a salt such as calcium chloride, can be added to the mixture. In addition to calcium chloride, such salts as barium chloride, manganous, and cerium chloride may be employed. 'I'he role played by the salt during the reaction period is not definitely known, although it is believed the reaction is catalytic in nature rather than any denite chemical reaction in view of the exceedingly'- small quantities required to produce results. As little as 116% of salt is ordinarily ample.

To produce the mixture, 4 parts of gelatin and 116% of calcium chloride are mixed together and reacted at elevated temperatures for approxi- 56 parts of diethylene glycol together with the glycol can be made, preferably with the assistance ofthe salt, and employed as a bonding agent in the manufacture of commercial safety glass, nevertheless it is my opinion that the addition of a diluent such as distilled water is to be i preferred because by including the diluent in the mixture, less skill is required in the assembling of the glass to get completely satisfactory'results.

i The same results are not obtained in making ofj avsolution by simply mixing. all of the ingredients of diethylene glycol 56 parts, water 40 parts, and gelatin 4 parts, plus l115% by weight calcium chloride and then heating. Such a mixture behaves entirely diilerently from a mixture produced by first reacting the water soluble adhesive, the solvent, and the salt, and then adding the water as above outlined.

Referring again'to the drawing, .in Fig. 1 is illustrateda type of machine that can be used in applying my improved mixture to the laminations. This isv one of the advantages to be gained by the yuse of this mixture, namely, the ability to satisfactorily apply the same to the laminations by mechanical means in contra-distinction to application by spraying or otherwise. It is not to be inferred that I limit myself to the use of such a machine because the bonding material can be applied to the laminations in any preferredmanner.o The advantages of the coating machine illustrated, however, among other things, reside in the abilityto control rather accurately the character of the deposit upon the laminations and the reduction/to a minimum of the possibility of dirt introduction between the laminations.

In Fig. 1, the numeral 15 designates a receptacle adapted to contain my improved bonding mixture 16. 'Ihe receptacle l5 has a discharge outlet 17, the effective opening of which is controlled by the adjusting mechanism 18.v Mounted beneath the discharge outlet or spout of the hopper is a pair ofrolls 19 and 20 positioned to create a pocket which receives the bonding mixture. Mounted in operative association with the roll'20 is a third roll 21 beneath which is placed the rotatable roll 22. The roll 22 is one of a series forming a conveyor adapted to support and move the glass sheet 23 between the rolls 21 and 22.

The rolls 19, 20 and 21 are illustrated in spaced relation for the purposes of illustration, and the bonding material is shown in a iilm 24. In actual practice, the rolls contact one another and the bonding agent completely coversthe peripheries of all of the three rolls. It has been found that a combination of metal and rubber rolls will give very satisfactory results. The deposit 25 of maferial upon the glass sheet 23 is controlled by the relative positions of the rolls 19, 20 and 21 and also vthe relative /position of the rolls 21 and-22. s

After the glass sheet Vhas passed through the coating machine, it is not 'necessary to dry or season the same, but' it can be used immediately. Thus, in Fig. 2, the two .coated sheets of glass have arranged therebetween the pyrOXylin plastic layer 13. This assembly forms what is known in the art 'asa sandwich. At the time the sandwichirmade, the kbonding material 14 on the,

. 1,9es,oo2

glass is wet and because of the ability to promptly assemble the coated glass, the possibility of dirt entering into the sandwich is further minimized. l

After arranging the laminations in sandwch form, they may be pressed in any preferred manner to give a finished composite structure. In the drawing, a series of rolls are shown in Fig. 3 which serve as pre-pressing rolls. The sandwiches may be carried on the conveyor 26 between the series of pairs of rolls 27 formed from a compressible material such as rubben 'Ihe rolls 27 are positively driven and adjusted to give the necessary pressure to the sandwich to bring the inner surfaces thereof into intimate contact. In so doing, noncondensable gases are excluded from between the laminations. Temperature controlling devices`28 can be arranged in the chamber 29, although this is not necessary in al1 cases.

After the treatment in the apparatus of Fig. 3, the sandwich may be further pressed in the platen press 30. .From the press 30, the glass may go to the autoclave 31.'

The autoclave consists of a casing 32 in which may be arranged the heat exchanger system 33 and an agitating device 34. The sandwiches can be placed in a rack 35 movable into and out of the autoclave upon removal of the top 36. In operation, the glass is placed in th`e autoclave which is closed, and a iiuid under pressure can be circulated through the conduits 37, and by reasonof the heat exchanger system, the temperature thereof can be controlled. While in the auto-- clave, the glass can be subjected to a pressure of about 200 poundsl per square inch for a perlod'of twelve to fifteen minutes and at a temperature of substantially 250 F.

Upon the removal of the glass from the autoclave, the marginal portions may be undercut and a weather-resisting seal 38 applied. This is shown diagrammatically in Fig. 6. `Whi1e the coatings 39 are shown in Fig. 6, in actual practice the bonding material is not discernible in the finished product.

As hereinabove pointed out, I depend not only on the adhesive characteristics of the water soluble adhesive for bonding action, but also employ the solvent action of the solvent part of the mi.

ture on the pyroxylin plastic to assist in giving a satisfactory bond between the laminations. The adhesive part of the mixture adheres very closely to the glass sheets, while the solvent constituent attacks' the pyroxylin plastic particularly upon the-elevation of temperature during the`pressing cycle in'a manner to bring about a very closel union between the various laminations.

While the process has been described by setting forth that tHe coating is applied to the surface of the glass, it will of course be appreciated that this coating can be appliedto the surfaces of the non-brittle material as well as to the surfaces of the glass, or both. a

With further reference to the bonding material, it may be well to point out that while the 40 parts of water appears to be quite substantial, the question of amounts is pertinent, and because of the very thinfilm that is applied to the glass. the small amount of water added as a diluent is readily absorbed during the laminating cycle so that the solvent responsible for the nitro-cellulose adhesion plays an important part in the resulting bond.

As above pointed out, I prefer that the pyroxylin plastic used be treated prior to lamination in a humidiiied atmosphere whereby to accurately control, within certain limits, the water content of the pyroxylin plastic.V The amount of water added in the bonding-agent is of course ltaken into consideration, but this vis rather negligible insofar as the total amount of moisture contained in the laminated sheet is concerned. Onthe other hand, the addition of the water is employed as a diluent. v

In commercial practice, after the glass sheets have been coated, the pyroxylin plastic is assembled between the glass sheets and oftentimes the operators willv not get the pyroxylin plastic properly. positioned .the rst time so that it is necessary to shift the plastic with respect to the glass. Where an undiluted mixtureis used, there is at times a tendency for the plastic to stick to the glass, causing difllculty in moving 'thereof with respect to the glass. By adding the diluent, this condition is not as noticeable and therefore the operators can more readily line up the laminations for proper position.

In addition t`o the use of diethylene glycol,

other polyglycols may be used, and I have in mind particularly polyglycols having higher molecular weights as for example, tri, tetra, and penta ethylene glycols. It may be that with the use of such polyglycols, the amount of rdiluent added can b e either reduced or entirely eliminated.

As above pointed out, the water diluent shouldA not be added to the mixture until after the gelatin and diethylene glycol have been reacted in the manner described. f

While 40 parts of water have given very satisfactory results, the lamount'of diluent is of course dependent upon the particular solvent used in the mixture, the amount of solvent, the temperature atwhich it is applied and the particular degree of solvent action desired. Therefore, a greater or lesser amountof water or other diluent can be used as desired.

It is to be understood that the form of the invention herewith described is to be taken as the preferred embodiment of thel same and that -various changes in the ingredients and proportions may be resorted to without departing from the spirit of the invention or the scope of the subjoined claims. g

I claim: l. 'I'he process of producing safety glass, consisting in reacting a mixture of gelatin and a polyglycol, Athen adding water' thereto, and depositing such solution on one surface each of two sheets of glass, interposinga translucent plastic layer between the coated surfaces of the two glass sheets, and then subjecting the sand-l wich thus formed to the combined action of heat and pressure to produce a composite structure.

2. The process of producing safety glass, consisting in reacting a mixture of gelatin, diethylene glycol, and a salt, then adding water thereto, and

depositing such solution -on one surface each of two sheets of glass, interposing a translucent plastic layer between the coated surfaces of the two glass sheets, and then subjecting the sandwich thus formed to the combined action of heat and pressure to produce a composite structure.

3. The process of producing safety glass, consisting in reacting a mixture of gelatin, diethylene glycol, and calcium chloride, then adding water` thereto, and depositing such sol'ution on one surface each of two sheets of glass, interposing a translucent plastic layer between the coatedsurfaces of the two glass sheets, and then subjecting the sandwich thus formed tothe combined action of heat and pressure to produce a composite structure.

4.- The process of producing safety glass, consisting in reacting a mixture of gelatin and diethylene glycol in a ratio of 4to 56, then adding 4,0 parts of water, and depositing such solution on one surface each of two sheets of glass, interposing a translucent plastic layer between the coated surfaces of the two glass sheets, and then subjecting the sandwich thus formed to the combined action of heat and pressure to produce a com-A posite structure.

5. The process of producing safety glass, consisting in reactinga mixture of gelatin and diethylene glycol in the ratio of 4to 56 in the presence of a small amount of salt at elevated temperatures, then adding 40 parts ofwater, and depositing such solution on'one surface each of two sheets of glass, interposing a translucent plastic layer between the coated surfaces of the two glass sheets, and then subjecting the sandwich thus lformed to the combined action of heat and pressure to produce a composite structure.

6. 4As a new article of manufacture, a'sheet of safety glass, consisting of two sheets' of glass and an interposed translucent plastic .membrane bonded together by the aid of a mixture of gelatin and diethylene glycol reacted togetherv and to which water is added as a diluent after said reaction has taken place. i

7. As a new article of manufacture, a sheet of l safety glass consisting of two sheets of glass and an interposed pyroxylin plastic layer bonded together by the aid of a mixture of gelatin, diethylene glycol, a salt, and a diluent.

8. As a new article of manufacture, a sheet-of safety glass consisting of two sheets of glass and an interposed pyroxylin plastic layer bonded together by the aid of a mixtureof gelatin,y di'- ethylene glycol, a salt, and water.

9. As a new article of manufacture, a sheet of safety glass consisting of two sheets of glass and an interposed pyroxylin plastic layer bonded together by the aid of a mixture of gelatin, diethylene glycol, and water in the approximate ratio of 4 to 56 to 40.

- GEORGE B. WATKINS. 

